August 28, 2013

Who knew you could use the guts of a power transistor as a solar cell! Steven fromRimStar even takes it a step further and chains five 2n3055 in a base to collector configuration to generate enough voltage to power a small calculator. Funny how some electronics form China are working fakes. The small calculator he got has a small solar cell in it already but once the case was cracked open it turned out that the calculator was simply powered by a small coin cell battery. I wonder if the solar cell was a fake or they were just too lazy to hook it up.

“To easily make a homemade/DIY solar cell, get a power transistor like the 2N3055 and carefully cut open the case. That exposes the semiconductor material inside to light. Hook up some wires and you’re done! Doing this I managed to get around 500 millivolts and 5.5 milliamps which is 2.7 milliwatts.”

3 Responses to “Calculator Powered by a Transistor Solar Cell”

In a simple circuit, the better way to measure the power output of anything is to use two meters at the same time: a voltmeter at the source and an ammeter connected in series with the load in the circuit. Here, he is shorting out the solar cell with the ammeter to get a current reading, then multiplying the open circuit voltage times the short circuit current to get the power output of the solar cell. In fact, the voltage across the ammeter connections will likely be significantly less than the open circuit voltage. Unless the solar cell has infinite power capacity and an internal resistance of zero ohms, the power generated by the solar cell will likely be significantly less than the calculated method. IMHO, the internal resistance of the solar cell and the internal resistance of the ammeter need to be taken into account when taking the readings.

Transistors will also act as LED’s when powered too. I discovered that by accident when I cut the metal can off of one while it was still in circuit. Very dim, but you can see it in a normally lit room, maybe cup your hands over it.

A lot of people don’t realize, when it comes to electronics/electricity, there’s a lot of yin/yang. Like Thermocouples. The produce electricity when heated or cooled, but they’re also the basic for thermoelectric heat pumps too. LED’s being emitters, and sensors at the same time.

I likewise cracked open a cheapie-chinese ‘solar cell’ powered battery to find that it was powered only by a button cell. The solar cell was hot melted into place without any wiring into the calculator itself whatsoever. It seems it is cheaper for them to fill the gap with a solar cell than it is to make another mould without the gap. Funnily enough, the solar cell wasn’t a fake either and made a healthy 0.7v under indoor lighting.